Fixing usage of XCTest framework (#89)

Author: letatas

Mocker.podspec

@@ -16,4 +16,5 @@ Pod::Spec.new do |spec|
   spec.ios.deployment_target = '10.0'
   spec.source_files = 'Sources/**/*'
   spec.swift_version = '5.1'
+  spec.frameworks = 'XCTest'
 end